Dual 7" Servo

MartinClan · #1 13th January 2012, 07:20

I'm confused.

If the metro servo works with the BMW master cylinder then why not the Dual Servo? The plunger arrangment in the Metro servo looked quite similar to that of the dual servo when I looked at my spare metro servo last night.

As I remember the operating rod on the master cylinder is hollow and the plunger from the servo goes up the middle.

Cheers

Robin

Edit:
OK - I looked at the picture of the cutway servo. I can see the problem now. The dual servo has a seat that the metro servo didn't have. The metro servo relying on the tip of the push rod instead.

GreatOldOne · #2 13th January 2012, 07:25

That's right, Robin. But the dual servo has an M6 threaded pushrod that you can lengthen or shorten to ensure that there is no slack before the pushrod hits the master cylinder.

MartinClan · #3 13th January 2012, 07:36

Before we all go and buy new master cylinders wouldn't it be worth:

1. Working out how much the push rod can move when the brake pedal is flat on the floor.

2. If, in this position there would still some operating rod visible on the master cylinder, then it would be safe to shorten it.

However I guess that shortening it may not be that easy. From its color I guess that the operating rod is made of a high carbon steel. Will probably need a cutting disc in an angle grinder.

Robin

Mike · #4 13th January 2012, 08:11

Guys

Please be careful.

The brake master cylinder has to be one of the most significant safety critical items on any car. Embarking on a procedure to cut and carve must be undertaken with great care.
Suitable new master cylinders are available for £30-40: is it really worth the effort, and risk?
Mike

Quote:

Originally Posted by MartinClan

Before we all go and buy new master cylinders wouldn't it be worth:

1. Working out how much the push rod can move when the brake pedal is flat on the floor.

2. If, in this position there would still some operating rod visible on the master cylinder, then it would be safe to shorten it.

However I guess that shortening it may not be that easy. From its color I guess that the operating rod is made of a high carbon steel. Will probably need a cutting disc in an angle grinder.

Robin

morris · #5 13th January 2012, 11:29

this was my background thought. Taking 10mm off the end would be straight forward and low risk but I think that 25mm will see the push rod go well past the outer edge of the M/C. If we could get some extra adapters made up you could layer up another 2 and then it's just a 15mm cut. it will start to look a bit rubbish though.

The only problem I can see with moving over to a Ford M/C (apart from the fact we're not sure which one to go for) is that although new cylinders are available on ebay, I've not found a single reservior. This is fine for those with remotes but no good if you want to go the traditional route. I think if we can nail down the correct Ford M/C then as you say, it's more than worth the extra £40 to do the job properly.

Quote:

Originally Posted by Mike

Guys

Please be careful.

The brake master cylinder has to be one of the most significant safety critical items on any car. Embarking on a procedure to cut and carve must be undertaken with great care.
Suitable new master cylinders are available for £30-40: is it really worth the effort, and risk?
Mike

MartinClan · #6 13th January 2012, 12:45

Perhaps someone has an old BMW master cylinder that can be stripped to see what's what?

If we can't do that then I agree a new master cylinder of an alternative design is the best bet.

Jason - does your master cylinder have any ID on it at all that might give a clue as to its origin?

Robin

mashtun · #7 13th January 2012, 14:12

Quote:

Originally Posted by MartinClan

Perhaps someone has an old BMW master cylinder that can be stripped to see what's what?

I'm stripping a 1994 E36 at the moment and I've got no need for the master cylinder - I'm happy to take it to pieces and take measurements/photos if it'll help someone...

Mark.

Mike · #8 13th January 2012, 13:27

Ian

Reservoirs are available in scrapyards on old Sierras, and more modern Fords. I'm told Sierras are scarce down South, but readily available in t' North.

Mike

Quote:

Originally Posted by morris

The only problem I can see with moving over to a Ford M/C (apart from the fact we're not sure which one to go for) is that although new cylinders are available on ebay, I've not found a single reservior. This is fine for those with remotes but no good if you want to go the traditional route. I think if we can nail down the correct Ford M/C then as you say, it's more than worth the extra £40 to do the job properly.

cabrioman · #9 13th January 2012, 13:46

Quote:

Originally Posted by MIKE

Simon Gregory fitted one from an XR4i and said it is good. Peter Morris fitted one from a 1.8 LX Sierra one and said it was good too! The smaller the diameter, the better the brake pressure will be: the down side being more pedal travel for the same effect.

The situation with the Ford master cylinder is even worse than you imply. There are also two very different flange sizes and hole centres! I beleive the better one to get is Lucas Girling, and not the Bendix one. The adaptor plate has been supplied with an etched 70mm pcd for the smaller flanged BMC, with holes at 70mm centres (Lucas Girling? - please check first though).
I have seen ones like I chose advertised for Transit Vans. John Tootle (Cabrioman) was going to investigate this - don't know how far he got.

As Mike has said I decided to swap my Hunter M/Cyl with remote reservoir back to a standard Sierra M/Cyl with the reservoir mounted on the cylinder as per Mikes. Fortunatly I had one in the garage as a spare from my original Cabrio donor Sierra, a 1992 Sierra 2.0 LX. The only marks on the cylinder are a stamp stating "22" which I understand is the bore size in mm. This is the same cylinder Pete Morris had fitted to his car, again taken from a standard Sierra.

I would think an enquiry at a local motor factors would turn up the correct cylinder (I am prety certain mine is a girling), the difficuly maybe the reservoir. That said although I have not tried it the cylinder I have with the directly mounted reservoir looks like it would take the pipe outlets Marlin used for the remote setup, so that may be a possibility.

John

Mike

I have sent you a PM regards my servo kit.

John

Mike · #10 13th January 2012, 07:51

Dear confused

The dual servo is a sealed unit, and has a closed recess of only 25mm deep.

Mike

Quote:

Originally Posted by MartinClan

I'm confused.

If the metro servo works with the BMW master cylinder then why not the Dual Servo? The plunger arrangment in the Metro servo looked quite similar to that of the dual servo when I looked at my spare metro servo last night.

As I remember the operating rod on the master cylinder is hollow and the plunger from the servo goes up the middle.

Cheers

Robin

Edit:
OK - I looked at the picture of the cutway servo. I can see the problem now. The dual servo has a seat that the metro servo didn't have. The metro servo relying on the tip of the push rod instead.